1. Field of the Invention
The present invention relates to a magnetism measuring apparatus for measuring or observing an amount of magnetism in a range of a micrometer with regard to a sample comprising a semiconductor element, semiconductor material or superconductive material, or metal material or inorganic material, and more particularly relates to a superconductive quantum interference element (hereinafter, referred to as SQUID) having a high resolution for detecting magnetism.
2. Description of the Related Art
Recently, there has been reduced into practice, a high sensitivity magnetic flux meter having a spatial resolution on the order of a micrometer which is referred to as a SQUID microscope and there has frequently been carried out measurement or observation by using a SQUID microscope with regard to various elements or materials. A SQUID is applied conventionally as a magnetism sensor having a high magnetic field resolution and when a SQUID is used as a SQUID microscope for observing magnetism of a very small region, the spatial resolution becomes an important function.
FIGS. 2A and 2B are on a outline circuit pattern diagram showing an example of conventional SQUID in consideration of spatial resolution, The SQUID is a DC-SQUID fabricated by a superconductive loop 10 and a feedback modulation coil 20. FIG. 3 shows an outline equivalent circuit diagram of the superconductive loop 10 shown in FIG. 2A. The superconductive loop 10 is constituted by a washer coil 11, two Josephson joints or junctions 12 and a detecting coil 13. As shown by FIG. 2A, the superconductive loop 10 is integrated on a silicon substrate along with the feedback modulation coil 20.
As the Josephson joint or junction 12, there is frequently used a tunnel junction type Josephson junction of niobium/aluminum oxide/niobium.
The feedback modulation coil 20 is magnetically coupled with the washer coil 11. Numeral 16 designates a contact hole of the detecting coil 13 and the washer coil 11.
In FIG. 2A and FIG. 3, by an outside control circuit, pertinent bias current is applied between two electrodes 21a and 21b of the washer coil 11 in directions designated in FIG. 3 and magnetic flux having an amount the same as that of magnetic flux detected by the detecting coil 13 and in direction reverse thereto, is fed back to the washer coil 11 via the feedback modulation coil 20 (not illustrated in FIG. 3) overlapping the loop of the washer coil 11 to drive the device. Thereby, the magnetic flux detected by the detecting coil 13 can be provided from the outside control circuit as a voltage output.
The spatial resolution is determined by a shape such as a size of the detecting coil constituting the SQUID and a distance between a sample and the SQUID. When a SQUID having high spatial resolution is designed and fabricated, the SQUID is fabricated by designing an effective detection area of the detecting coil to be as small as possible and utilizing thin film fabricating technology by using photolithography technology.
According to the related art SQUID described above, when the detecting coil is intended to be small in order to promote the spatial resolution, in comparison with an inner diameter of the detecting coil, a width of the detecting coil per se and a superconductive film at a vicinity of the detecting coil are enlarged relatively. As a result, there is a problem in that other than magnetism coupled to the inner diameter portion of the detecting coil, there are detected portions of magnetic flux repelled by the diamagnetism of the detecting coil per se or the superconductive film at a vicinity of the detecting coil and, as a result, an effective area of the detecting coil is enlarged.
It is an object of the invention to resolve the above-described problem and to provide a SQUID with a reduced effective detection area of a detecting coil and high spatial resolution.
According to the invention, in order to solve the a detecting coil of SQUID showing Embodiment 1 of the invention;
(Second Means)
In addition to the first means, there is used a beam machining apparatus as apparatus of machining the slit.
According to SQUID by the first means, in the magnetic flux repulsed by the detecting coil and/or the superconductive film at the periphery of the detecting coil, a portion of extra magnetic flux which is going to couple with the detecting coil, passes through the slit without being coupled to the detecting coil and therefore, coupling of the extra magnetic flux to the detecting coil is reduced and therefore, the effective detection area of the detecting coil can be reduced and the spatial resolution can be promoted.
By the second means, micromachining of the slit can be carried out and therefore, the function of excluding the extra magnetic flux coupled to the detecting coil can be promoted and the spatial resolution can further be promoted.